A waterproof/breathable fabric is a textile that both repels water and allows air or water vapor to pass through. This is a stark contrast to traditional materials for rain jackets. In the past, people have worn rubberized nylon jackets. These offer a low price, but they have zero breathability and are quite heavy. There are two main types of waterproof/breathable fabric: coated/laminated, and microporous membrane. Coated fabrics (PreCip, Hyvent) are typically a nylon face fabric with a high abrasion resistance bonded to a waterproof layer. This offers an economic choice and moderate performance. Some fabrics (eVent, Gore-Tex) have a microporous membrane bonded to a face fabric. These products have drastically higher prices, waterproofness and breathability ratings. These utilize Polytetrafluoroethylene, a fluorocarbon with some very unique properties.
Coated and laminated fabrics fall into three categories: microporous, monolithic, or bicomponent. Microporous coatings and laminates (not membranes) are typified by poor breathability and poor durability. This is because the coating is applied while liquid, causing inconsistent thickness. Once the laminate or coating starts to crack, it is difficult to stop. Monolithic coatings are applied as one thin, unified, and solid sheet. This means that performance is good while the fabric is new, but durability is poor. Bicomponent coatings and laminates combine both microporous layers and monolithic layers. This means that the waterproofness of the product will last much longer, but breathability is poor due to the thickness of the water barrier. Fabrics that are simply a waterproof layer bonded to the face fabric are 2 layer fabrics. Some feature a spray-on texture to the waterproof layer such as DryTouch Ceramic. This feels more comfortable because it raises the coating off the skin. Others laminate a third layer to the inside to enhance abrasion resistance. Therefore, coated fabrics come in 2, 2.5, and 3 layer thicknesses.
Textiles featuring waterproof/breathable microporous membranes also come in 2, 2.5, and 3 layer fabrics. Microporous membranes are porous, but pore sizes are so small that they bar larger molecules 2.5 layer fabrics are rare, the foremost being Gore-Tex Paclite Shell. This is formed by laminating a sheet of carbon (often from bamboo) to the interior of the fabric, under the face fabric and membrane. Fabrics with waterproof/breathable membranes run from $150 to $550 MSRP. This is because all membranes are constructed from PTFE, which is difficult to create. The gold-standard of waterproof/breathable fabrics is Gore-Tex, manufactured by W. L. Gore & Associates. Gore-Tex features over nine billion pores per square inch. These pores are twenty thousand times smaller than a drop of water. They are smaller than the actual water molecule, which means that waterproofness is absolute. The pores are, however, seven hundred times larger than the size of a molecule of water vapor. This means that liquid water (rain) is repelled by the textile, while gaseous water (perspiration) is free to pass through. Because of this, fabrics featuring a microporous membrane offer the highest levels of breathability and waterproofness. All membranes are produced from PTFE, which is expensive to make and refine. They are primarily used in situations when performance is critical, due to their inherent expense.
Discovered by a fortuitous accident in 1938 by chemist Roy Plunkett, PTFE quickly found many uses. Plunkett was trying to create a new refrigerant, but instead his perfluoroethylene polymerized in an iron container. The iron served as the catalyst. PTFE has the second lowest coefficient of friction of any known solid (Diamond carbon having the lowest), and because of this Marc Grégoire and Marion Trozzolo soon popularized “non-stick” pans. PTFE was further researched during the Manhattan Project, which used PTFE to contain highly reactive chemicals. PTFE excels at this because it is chemically inert. It is highly biocompatible, so it is used for piercings and reinforcements to blood vessels. PTFE is also a premium dielectric insulator because it has a high melting point and is easy to mold. PTFE is prone to “creep” (when a solid will slightly mold to it’s environment) making it a good choice for a washer or seal when under some pressure. PTFE’s tendency to creep means a better fit and a better seal. Marketed under the brand name Teflon (manufactured by DuPont), PTFE is occasionally used in architecture because of its high tensile strength (when taut) and resistance to corrosion. Many armor-piercing bullets are coated with PTFE. This lowers the friction between the bullet and the inside of the barrel of the rifle, and therefore it preserves the gun’s rifling.
Polytetrafluoroethylene is the flurocarbon form of tetrafluoroethylene formed through emulsion polymerization. Emulsion Polymerization contributes to PTFE’s high molecular weight. PTFE is a very long carbon chain (50,000 carbons or more) where every hydrogen atom has been replaced by a fluorine atom. Because of the high electronegativity of fluorine, this bond is incredibly strong and renders PTFE almost totally chemically inert. This also contributes to the chemical’s low coefficient of friction and resistance to van der Waals forces. In fact, PTFE is so uniquely resistant to van der Waals forces that geckos are unable to cling to its surface. Insects, notably ants, are also unable to stick to PTFE for the same reason.
Expanded PTFE, or ePTFE is primarily used in performance rainwear. Discovered by Robert W. Gore in 1969, ePTFE is created by stretching heated solid rods of PTFE. It becomes malleable, and then can be drawn into a uniformly thin sheet. W. L. Gore & Associates is the sole manufacturer of Gore-Tex, a product of ePTFE. W. L. Gore uses a proprietary method to create nine billion pores per square inch in the ePTFE.
PTFE makes waterproof/breathable fabrics more complex, but much more effective. Materials like Gore-Tex have breathability ratings from 30k to 40k g/m2/24 (the unit that measurability is measured in) hours, whereas a coated or laminated textile like Hyvent may be around 12k to 15k. Because of the difficulty in refining and creating PTFE and ePTFE, these materials tend to be more expensive.
Whether rain gear is waterproofed by a microporous membrane or a laminate, the face fabric is typically treated by DWR. DWR (durable water repellent) is a silicon based polymer that is either sprayed on or washed into the fabric. When it has coated the nylon face fabric, it lowers the surface tension so much that water beads up instead of clinging. Even though DWR is not what actually waterproofs the garment, it is critical to performance. This because if the face fabric gets too wet, it won't breathe well. Once water has soaked the face fabric, breathability plummets and water vapor (from the wearer's body) builds up on the inside. Many people assume that this means that water has penetrated the fabric. This is incorrect. Even if the laminate or membrane remains intact, moisture from lack of breathability will build up. This is called "wetting-out".
For my experiment, I intend to experiment with the two main types of DWR and test their performance. I will test the breathability, waterproofness, and ability to make water bead.
Procedure
I started with an old (purchased approximately 8 years ago) REI Rain Jacket. It had a nylon face fabric with a white coating of Polyurethane. It also had a fabric backing to enhance abrasion resistance. After studying wear patterns on rain shells, I decided that it is likely that the left side and the right side are more equal than the top and the bottom. I chose to take my fabric samples from the back because the fabric was the most pristine and there were no seams to weaken the structure.
Table of Contents
Polytetrafluoroethylene and DWR
George Van Horne
The Uses and Chemistry of Polytetrafluoroethylene
A waterproof/breathable fabric is a textile that both repels water and allows air or water vapor to pass through. This is a stark contrast to traditional materials for rain jackets. In the past, people have worn rubberized nylon jackets. These offer a low price, but they have zero breathability and are quite heavy. There are two main types of waterproof/breathable fabric: coated/laminated, and microporous membrane. Coated fabrics (PreCip, Hyvent) are typically a nylon face fabric with a high abrasion resistance bonded to a waterproof layer. This offers an economic choice and moderate performance. Some fabrics (eVent, Gore-Tex) have a microporous membrane bonded to a face fabric. These products have drastically higher prices, waterproofness and breathability ratings. These utilize Polytetrafluoroethylene, a fluorocarbon with some very unique properties.
Coated and laminated fabrics fall into three categories: microporous, monolithic, or bicomponent. Microporous coatings and laminates (not membranes) are typified by poor breathability and poor durability. This is because the coating is applied while liquid, causing inconsistent thickness. Once the laminate or coating starts to crack, it is difficult to stop. Monolithic coatings are applied as one thin, unified, and solid sheet. This means that performance is good while the fabric is new, but durability is poor. Bicomponent coatings and laminates combine both microporous layers and monolithic layers. This means that the waterproofness of the product will last much longer, but breathability is poor due to the thickness of the water barrier. Fabrics that are simply a waterproof layer bonded to the face fabric are 2 layer fabrics. Some feature a spray-on texture to the waterproof layer such as DryTouch Ceramic. This feels more comfortable because it raises the coating off the skin. Others laminate a third layer to the inside to enhance abrasion resistance. Therefore, coated fabrics come in 2, 2.5, and 3 layer thicknesses.
Textiles featuring waterproof/breathable microporous membranes also come in 2, 2.5, and 3 layer fabrics. Microporous membranes are porous, but pore sizes are so small that they bar larger molecules 2.5 layer fabrics are rare, the foremost being Gore-Tex Paclite Shell. This is formed by laminating a sheet of carbon (often from bamboo) to the interior of the fabric, under the face fabric and membrane. Fabrics with waterproof/breathable membranes run from $150 to $550 MSRP. This is because all membranes are constructed from PTFE, which is difficult to create. The gold-standard of waterproof/breathable fabrics is Gore-Tex, manufactured by W. L. Gore & Associates. Gore-Tex features over nine billion pores per square inch. These pores are twenty thousand times smaller than a drop of water. They are smaller than the actual water molecule, which means that waterproofness is absolute. The pores are, however, seven hundred times larger than the size of a molecule of water vapor. This means that liquid water (rain) is repelled by the textile, while gaseous water (perspiration) is free to pass through. Because of this, fabrics featuring a microporous membrane offer the highest levels of breathability and waterproofness. All membranes are produced from PTFE, which is expensive to make and refine. They are primarily used in situations when performance is critical, due to their inherent expense.
Discovered by a fortuitous accident in 1938 by chemist Roy Plunkett, PTFE quickly found many uses. Plunkett was trying to create a new refrigerant, but instead his perfluoroethylene polymerized in an iron container. The iron served as the catalyst. PTFE has the second lowest coefficient of friction of any known solid (Diamond carbon having the lowest), and because of this Marc Grégoire and Marion Trozzolo soon popularized “non-stick” pans. PTFE was further researched during the Manhattan Project, which used PTFE to contain highly reactive chemicals. PTFE excels at this because it is chemically inert. It is highly biocompatible, so it is used for piercings and reinforcements to blood vessels. PTFE is also a premium dielectric insulator because it has a high melting point and is easy to mold. PTFE is prone to “creep” (when a solid will slightly mold to it’s environment) making it a good choice for a washer or seal when under some pressure. PTFE’s tendency to creep means a better fit and a better seal. Marketed under the brand name Teflon (manufactured by DuPont), PTFE is occasionally used in architecture because of its high tensile strength (when taut) and resistance to corrosion. Many armor-piercing bullets are coated with PTFE. This lowers the friction between the bullet and the inside of the barrel of the rifle, and therefore it preserves the gun’s rifling.
Polytetrafluoroethylene is the flurocarbon form of tetrafluoroethylene formed through emulsion polymerization. Emulsion Polymerization contributes to PTFE’s high molecular weight. PTFE is a very long carbon chain (50,000 carbons or more) where every hydrogen atom has been replaced by a fluorine atom. Because of the high electronegativity of fluorine, this bond is incredibly strong and renders PTFE almost totally chemically inert. This also contributes to the chemical’s low coefficient of friction and resistance to van der Waals forces. In fact, PTFE is so uniquely resistant to van der Waals forces that geckos are unable to cling to its surface. Insects, notably ants, are also unable to stick to PTFE for the same reason.
Expanded PTFE, or ePTFE is primarily used in performance rainwear. Discovered by Robert W. Gore in 1969, ePTFE is created by stretching heated solid rods of PTFE. It becomes malleable, and then can be drawn into a uniformly thin sheet. W. L. Gore & Associates is the sole manufacturer of Gore-Tex, a product of ePTFE. W. L. Gore uses a proprietary method to create nine billion pores per square inch in the ePTFE.
PTFE makes waterproof/breathable fabrics more complex, but much more effective. Materials like Gore-Tex have breathability ratings from 30k to 40k g/m2/24 (the unit that measurability is measured in) hours, whereas a coated or laminated textile like Hyvent may be around 12k to 15k. Because of the difficulty in refining and creating PTFE and ePTFE, these materials tend to be more expensive.
Whether rain gear is waterproofed by a microporous membrane or a laminate, the face fabric is typically treated by DWR. DWR (durable water repellent) is a silicon based polymer that is either sprayed on or washed into the fabric. When it has coated the nylon face fabric, it lowers the surface tension so much that water beads up instead of clinging. Even though DWR is not what actually waterproofs the garment, it is critical to performance. This because if the face fabric gets too wet, it won't breathe well. Once water has soaked the face fabric, breathability plummets and water vapor (from the wearer's body) builds up on the inside. Many people assume that this means that water has penetrated the fabric. This is incorrect. Even if the laminate or membrane remains intact, moisture from lack of breathability will build up. This is called "wetting-out".
For my experiment, I intend to experiment with the two main types of DWR and test their performance. I will test the breathability, waterproofness, and ability to make water bead.
Procedure
I started with an old (purchased approximately 8 years ago) REI Rain Jacket. It had a nylon face fabric with a white coating of Polyurethane. It also had a fabric backing to enhance abrasion resistance. After studying wear patterns on rain shells, I decided that it is likely that the left side and the right side are more equal than the top and the bottom. I chose to take my fabric samples from the back because the fabric was the most pristine and there were no seams to weaken the structure.
Results
Conclusions
References
1. Atkins, P. W. Molecules. No Publisher Listed. Print. Scientific American Library Ser.; #21.
2. Buthelezi, Thandi, Laurel Dingrando, and Nicholas Hainen. Chemistry: Matter and Change. New York, N.Y.: Glencoe/McGraw-Hill, 2008. Print.
3. Newton, David E. Chemistry of New Materials. New York: Facts on File, 2007. Print.
4. "Gore-Tex." Wikipedia, the Free Encyclopedia. Web. 20 Mar. 2010. <http://en.wikipedia.org/wiki/Gore_Tex>.
5. "Emulsion Polymerization." Wikipedia, the Free Encyclopedia. Web. 20 Mar. 2010.
a. <http://en.wikipedia.org/wiki/Emulsion_polymerization>.
6. "Polytetrafluoroethylene." Wikipedia, the Free Encyclopedia. Web. 20 Mar. 2010. <http://en.wikipedia.org/wiki/PTFE>.
7. "Creep." Wikipedia. Web. 20 Mar. 2010.
a. <http://en.wikipedia.org/wiki/Creep_(deformation)>
8. "Robert W. Gore." Wikipedia. Web. 20 Mar. 2010. <http://en.wikipedia.org/wiki/Robert_W. Gore>.
9. W. L. Gore & Associates. Web. 20 Mar. 2010. <http://www.gore.com/en_xx/index.html?RDCT=wlgore.com>.
10. Mcnett Waterproofing. Web. 20 Mar. 2010.
< http://www.mcnett.com:80/Default.aspx>
11. "Gore-Tex Product Training" 3point5.com . Web. 20 Mar, 2010. http://www.3point5.com/action/mfg/gore/playCourseModule?moduleId=1460&courseId=605&returnView=training (site is locked - log in necessary)